In gear oil applications, sulfurized olefins are typically used to protect gears from scoring. However, these sulfur compounds are extremely corrosive towards yellow metals, such as copper and copper alloys. The sulfur components in combination with phosphorus components produce a composition that degrades the copper. Gear oil specifications have minimum requirements for copper corrosion. For example, the API GL-5 category requires a maximum rating of 3 in the ASTM D-130 Test. However, this test does not provide a quantitative measurement of copper corrosion. It is a visual rating based on the discoloration of a copper strip. To obtain a quantitative measurement, we use the copper catalyst weight loss measurement from the ASTM D-5704 Test. The copper catalyst weight loss also reveals the copper corrosiveness of the oxidized oil.
Sulfurized isobutylenes are widely used in formulating gear lubricants intended for API GL-5 service. However, this type of sulfur-containing extreme pressure component causes large copper catalyst weight loss in the ASTM D-5704 test.
European Patent Application No. 678 569 B1 discloses a lubricating composition comprising a major amount of an oil of lubricating viscosity with an iodine number less than 4, (A) one or more ashless antioxidants selected from amine antioxidants, dithiophosphoric esters, phenol antioxidants, dithiocarbamates and aromatic phosphates, (B) from 0.01 to 3% by weight of at least one boron-containing dispersant or detergent, and optionally, (C) at least one additive selected from (i) a sulfur containing antiwear or extreme pressure agent, (ii) a phosphorus or boron antiwear or extreme pressure agent, and (iii) mixtures thereof, provided that (C) is different from (A), and wherein the total amount of antioxidant is from 2 to 10% by weight. The additives are useful for controlling oxidation of lubricants. Further, these lubricants have reduced viscosity increase caused by oxidation, while maintaining favorable carbon/varnish ratings.
U.S. Pat. No. 6,362,136 discloses compositions containing a sulfur-containing antiwear/extreme pressure agent, basic nitrogen compound or a mixture thereof together with a hydrocarbyl mercaptan. The composition may additionally contain a phosphorus or boron antiwear or extreme pressure agent, a dispersant or an overbased metal salt. This patent also relates to lubricants, functional fluids, and concentrates containing the same. Seals, e.g. nitrile, polyacrylate, and fluoroelastomer seals, in contact with these compositions have reduced deterioration. This patent teaches that with the use of these compositions, lubricants, and functional fluids, the seals useful life is extended.
U.S. Pat. No. 6,262,000 discloses that the antiwear performance of power transmitting fluids, particularly continuously variable transmission fluids, is improved by incorporating an additive combination of amine phosphates, organic polysulfides, zinc salts of phosphorothioic acid esters and optionally a friction modifier.
U.S. Pat. No. 5,254,272 discloses lubricant compositions especially useful as hydraulic fluids contain a metal-free anti-wear or load-carrying additive containing sulfur and/or phosphorus and an amino succinate ester as corrosion inhibitor. This patent teaches that such compositions are free from heavy metal and have improved environmental acceptability where heavy metals are to be avoided, e.g. in agriculture.
U.S. Pat. No. 5,342,531 discloses a lubricant composition comprising a major proportion of polyalkylene glycol of lubricating viscosity and a minor proportion dissolved therein of (a) at least one sulfur-containing antiwear or extreme pressure agent, (b) at least one amine salt of at least one partially esterified monothiophosphoric acid, and (c) at least one amine salt of at least one partially esterified phosphoric acid. This patent teaches that such compositions have improved resistance to wear, oxidative degradation and metallic corrosion.
U.S. Pat. No. 5,942,470 discloses gear oils and gear oil additive concentrates of enhanced positraction performance comprising: (i) at least one oil-soluble sulfur-containing extreme pressure or antiwear agent; (ii) at least one oil-soluble amine salt of a partial ester of an acid of phosphorus; and (iii) at least one oil-soluble succinimide compound. These compositions preferably contain one, more preferably two, and most preferably all three of the following additional components: (iv) at least one amine salt of a carboxylic acid; (v) at least one nitrogen-containing ashless dispersant; and (vi) at least one trihydrocarbyl ester of a pentavalent acid of phosphorus.
Japanese Patent No. JP 2000-328084 discloses a gear oil composition comprising a specified dialkyltrisulfide, a specified dithiophosphoric ester, and one or more of acidic phosphoric and phosphorus esters and alkylamine salts of the esters in a base oil of a kinematic viscosity at 100° C. The composition has high oxidation stability and corrosion resistance to copper at temperatures of 150° C. or higher.
U.S. Pat. No. 4,609,480 discloses a lubricant composition effective in extending the fatigue life and increasing the corrosion resistance of the machine parts lubricated therewith. The lubricant composition comprises two types of essential additives, namely (a) a dithiocarbamic acid ester and/or an alkyl thiocarbamoyl compound and (b) a 1,3,4-thiadiazole compound admixed with the lubricant base material each in a limited amount. In addition to the above mentioned advantages, the resistance against scoring can further be increased by the admixture of the lubricant composition with a third additive (c) such as sulfurized olefins, sulfurized oils, sulfurized oxymolybdenum dithiocarbamates, sulfurized oxymolybdenum organophosphordithioates, phosphoric acid esters and phosphorus esters.